Disclosed herein are apparatus and methods for detecting and quantifying contaminants in a liquid, and systems for use thereof.
The detection of trace (e.g., less than 1% by volume) and microtrace (e.g., less than 1.0×10−6% by volume) levels of chemical contaminants in aqueous solutions is important for monitoring the condition of numerous applications. For example, ultrapure water (i.e. water having a microtrace concentration of ionic species) is desirable in many industrial processes including, but not limited to, the semiconductor, pharmaceutical, agricultural, chemical, energy, and food processing industries. In one specific example, nuclear reactors can employ ultrapure water for cooling purposes. The ultrapure water can comprise contaminants, which cause corrosion and other problems in the reactors fluid handling system. Therefore, a system and method for detecting and quantifying these contaminants is extremely desirable.
The detection of chemical contaminants has evolved significantly over the last few decades. There are several techniques currently available for the detection and quantification of trace levels of ionic species in aqueous solutions. These techniques include ion chromatography (IC), inductively coupled plasma atomic emission spectrometry (ICP), mass spectrometry (MS), ICP-MS, and capillary electrophoresis (CE). Additionally, electrochemical, optical, and hybrid chemical sensors (e.g., combinations of different techniques such as surface plasmon resonance with anodic stripping voltammetry), have been applied for trace analysis of ionic species in water. Unfortunately, these methods can require extensive sample preparation or are limited by poor selectivity, inadequate detection limits, interference effects, baseline drift, and contamination during sampling or handling.
IC is the primary means of ionic species detection in aqueous solutions. For example, nuclear power plants have predominantly used in-line ion chromatography for routine monitoring of ionic species. IC methods originally comprised column ion exchange chromatography, which required large sample volumes, wet chemical analysis of collected fractions, and took hours to perform. More recently, IC methods have been developed that require significantly smaller sample volumes, operate virtually unattended under computer control, and can be conducted in only minutes. However, modern IC methods still suffer from disadvantages that make their use impractical in many situations, such as expense, complexity, and maintenance. Furthermore, the IC's currently attain an analysis time of approximately ten minutes, which is still too long in many applications.
ICP and ICP-MS are also used for ionic species detection. Inductively coupled plasma-isotope dilution mass spectrometry (ICP-IDMS) is suitable as a routine method for trace element and element speciation analysis; however, it is limited by the lack of commercially available isotope-labeled spike compounds for species-specific isotope dilution and by the complicated system set-up required for species-unspecific ICP-IDMS analysis. Therefore, there is a strong need to develop a more suitable detection method.
CE, which employs 10 to 100 times lower effluent volumes and provides a quicker measurement time than IC (typically less than a three minutes), is another common means of detecting ionic species. CE also has its limitations, e.g., there are practical limits to the amount of voltage that can be applied and to the shortness of the capillary tube. Further, the sample must be introduced in a band of finite width, and a finite volume is needed for reliable detection. Additionally, the heating of the electrolyte in the tube due to extremely high voltage gradients causes problems, such as undesirable zone broadening or even boiling of the electrolyte and a total breakdown of the electrophoretic process. Such limitations make the use of capillary zone electrophoresis impractical for many applications.
In light of the drawbacks associated with the current techniques employed for the detection and quantification of species in aqueous solutions, there is a current need for a detection method and a detection system that is free from the aforementioned limitations as well as limitations such as significant interference effects, baseline drift, and unintended water contamination due to handling.